A model that looks affordable on paper can still fail on your own hardware for one simple reason. It does not fit in memory. The download size is only part of the story. The weights take space, the precision changes how much space they take, and a long conversation adds memory on top as the conversation grows. A short test prompt can pass easily while a real session with a long document runs out of memory halfway through.
Before you choose a model, work out three numbers. First, how much memory the weights need at the precision you plan to use. Second, how much extra memory a long context will need. Third, how much headroom you want to leave for the system itself. If the total is close to your card limit, a smaller model or a lower precision may be the honest choice, not a compromise.
If you want to run those numbers quickly, this LLM VRAM calculator lets you change model size, precision, and context and see the memory figure move at once. Use it as a planning check, not as a hardware promise. Real usage varies, so recheck the model card before you commit to a setup.
And for the full set of free planning tools, visit AI Calculators.
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